1. Field of the Invention
The present invention relates to fuel supply systems and more particularly to a flow divider and ecology valve for supplying fuel to an engine manifold and withdrawing fuel therefrom upon engine shut-down.
2. Description of the Related Art
Gas turbine engine fuel delivery systems may require multiple fuel manifolds and an arrangement for apportioning fuel flow among those manifolds to segregate various types of fuel nozzles for optimal engine performance. For example, U.S. Pat. No. 5,809,771 to Wernberg discloses a fuel flow splitting valve having a single piston operable in two different regions, one for modulating flow to primary and secondary engine nozzles as a function of fuel pressure and another where flow to primary and secondary engine nozzles is determined by the fixed port geometry. Also, some engines may require an ecology function that removes a set quantity of fuel from the engine fuel manifold(s) upon cessation of engine operation. Fuel removal is required to keep fuel from vaporizing into the atmosphere and to avoid fuel coking on the engine's fuel nozzles, a condition that hinders nozzle performance. Prior art ecology systems have used an arrangement of pistons, check valves, plumbing, reservoirs and pumps to accomplish this task. In engines requiring multiple fuel manifolds, multiple ecology valves or a multiple chambered ecology valve have been used. A two chambered valve is disclosed in the abovementioned Wernberg patent. In the Wernberg system, fuel is simultaneously withdrawn from the two manifolds and a separate chamber is required for each engine manifold to ensure complete fuel removal from those manifolds upon engine shut-down. These types of architecture result in complex high cost and weight ecology systems.
It is desirable to minimize the fuel remaining in an engine intake manifold upon cessation of engine operation and to provide a compact, economical ecology function for fuel supply systems. It is also desirable to achieve such an ecology function by employing a simple valve which is controlled solely by fuel flow to the manifold(s) involved. It is further desirable to provide both an ecology function and a fuel flow dividing function in a common simplistic valve mechanism.